In each backcross generation, a hybrid is crossed with the elite parent. The amount of the wild parent genome passed on to the next generation will vary among offspring. The middle panel shows several of the possible chromosome complements that could be donated by the hybrid parent, each containing varying amounts of wild genes. In some offspring, even the disease resistance gene will not be passed on.
What we'd like to do, in each generation, is to select those individuals that received the largest amount of the recurrent parent genome, and also carry the desired gene (bottom panel). For this purpose, molecular markers can be used to keep track of both the gene of interest, as well as to distinguish between DNA from the donor parent, and DNA from the recurrent parent.
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